1. Field of the Invention
The invention relates to electro-optic conversion modules, and particularly to connecting rigid and flex circuit boards in parallel optical media converters.
2. Description of the Related Art
The speed of computers and the data transfer between them is ever increasing. Optical data transmission techniques have been developed to provide high capacity signal transmission without many of the physical limitations for electrical cables. Fiber-optic cables have advantageous transmission characteristics, which are utilized with optoelectronic devices such as fiber-optic transceivers by converting electrical signals into optical signals and vice versa at the ends of the fiber-optic cables.
The typical hardware architecture of computers involves circuit boards that are perpendicularly connected with a pin edge or a pin array in lengthy multi-pin connectors, which are laterally arrayed on a mother board. That way, the circuit boards are oriented parallel with their receptacle end showing towards the back end of the computer. The designated ends have mounting sites that carry the cable connectors. The cable connectors typically reach through open slots in the back face of the computer chassis such that the communication cables can be connected from outside.
The core of a fiber optic transceiver is an optoelectronic semiconductor-based module. The transceiver receives and emits light beams perpendicular to its top surface. Since the fiber cable is connected normal to the computer back face as other communication cables, the planar optoelectronic semiconductor preferably has a first distinct orientation which is perpendicular oriented to the circuit board.
To extend the application of the fiber optic transceiver for mass-produced, low-cost computers, it is desired for the individual components to be economical to fabricate, and for the assembly of the fiber optic transceiver to be simple and reliable at the same time. A number of attempts have been made to integrate some of these design considerations and others into a feasible opto-electronic transceiver module package. For example, U.S. Pat. No. 6,583,902, which is assigned to the same assignee as the present invention and is hereby incorporated by reference, describes an advantageous opto-electronic transceiver module package, as do others of the references cited and incorporated by reference below.
The optical transceiver of the present invention preferably comprises a parallel optical module that can convert four lane InfiniBand®, Cx4, four port or four channel signals into parallel optical signals. It can preferably interface with an industry standard media dependent interface (MDI) connector on the electrical side. In an MDI connector interface embodiment, the PCB thickness on the electrical side would be preferably about 40 mils. Thus, it is desired to have a rigid board design for making the electrical connection.
The optical transceiver of the present invention preferably can interface also optically interface according to an industry standard manufacturing production order (MPO), which is configured to be in parallel with a PCB surface. The parallel optical module generally uses a VCSEL array for its low cost. The VCSELs emit the light from their top surfaces. It is recognized in the present invention that a flex PCB may be advantageously used to turn the optical axis, which is normal to the plane of the board when VCSELs are used, into parallel with the rigid PCB surface. That is, the plane of the electrical connection end of the board is preferably orthogonal to the plane of the fiber optic coupling end of the board. Thus, a rigid board and a flex board are preferably both used, and it is therefore desired to have a way to couple them together mechanically, so that signals can be transferred between them.
One method would be to design a rigid-flex board such as that illustrated at FIG. 9, which is recognized by the inventors as a schematic illustration in accordance with an alternative embodiment of the invention. FIG. 9 shows a rigid-flex board, which is a single board that is rigid on one end 52 and that is around 40 mils thick for connecting with a standard MDI connector. The other end 54 of the board is flexible so that it can have an approximately 90° contour to cause the output of the VCSEL array to be parallel to the rigid board, and thus the plane of the end of the board containing the VCSEL array would itself be orthogonal to the rigid board. The interface coupling 56 would involve some form of adhesive or bonding material that adheres to both the rigid and flex materials, or two such materials that adhere to themselves and with each of the rigid and flex materials.
This concept illustrated at FIG. 9 is understandably expensive due to the difficulty in making the board, i.e., it tends to have undesirably long fab cycles. Details regarding implementation of this alternative approach are understood by those skilled in the art, and rigid-to-flex manufacturing may be accordingly obtained from HET, Inc. of Victoria, Minn. or Flex Interconnect Technologies, Inc. of Milipitas, Calif. Moreover, the resulting boards are also prone to have reliability issues. For example, the mechanical or signal coupling at the interface 56 can break down. Therefore, although FIG. 9 schematically illustrates an alternative embodiment that would work to implement rigid-to-flex interfacing to realize an optical transceiver in accordance with the invention, a more advantageous embodiment is described below in the Detailed Description of the Preferred Embodiments.